Improvement in the manufacture of steel by the open-hearth process



UNITED STATES PATENT OFFICE THOMAS S. BLAIR, OF PITTSBURG, PENNSYLVANIA.

IMPROVEMENT IN THE MANUFACTURE OF STEEL BY THE OPEN-HEARTH PROCESS.

Specification forming part of Letters Patent No. 155,136, dated September 22, 1874; application filed June 24, 1874.

To all whom it may concern:

Be it known that I, THOMAS S. BLAIR, of Pittsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Open-Hearth Process for Making Steel; and I do hereby declare the following to be a full, clear, and exact description thereof.

This invention relates to the production of cast-steel by the open-hearth process.

At the present time the most generallyadopted method is what is known as the Siemens-Martin process, in which a bath of castiron is first decarburized by the addition of wrought-iron, and finally recarburized by the addition of ferro-manganese and spiegeleisen.

The pig or cast iron bath is employed because the carbon contained renders the metal of easy fusion, and supplies whatever of that elementmay be necessary in addition to the quantity imparted by the triple compound of iron, carbon, and manganese used in the recarbonizing step.

The object of my invention is to provide a substitute, in whole or part, for the castiron heretofore employed; and to this end my method is to take iron sponge (such as is described in Letters Patent N 0. 126,924, granted to me May 21, 1872,) and mingle with it in any convenient way one or more of the substances known to produce rapid absorption of carbon by iron, in what is called case-hardening, together with the desired per cent. of finelypulverized carbon. The mixture thus formed can then be melted alone in the open-hearth furnace, or along with cast-iron previously fused.

The sponge used by me is the product obtained by treating oxides of iron in contact with carbon at a suitable heat, and out of contact with the atmosphere; it is practically metallic iron. It has an open spongy texture, whereby it is rendered extremely sensitive to chemical action, and this characteristic of the sponge I take advantage of to obtain a carburet of the desired grade or quality, the rationale of the operation being that the iron sponge, by virtue of its sensitiveness and the presence of the case-hardening substances, (such, for instance, as yellow prussiate of potash,) takes up carbon from the carbonaceous substance with which it is mixed before the temperature is sufficiently high to melt the mass. In this way, to whatever extent it thus acquires carbon, I dispense with the necessity of cast-iron.

My invention, therefore, consists in substituting iron sponge for cast-iron in the openhearth process, by imparting to the sponge the required per cent. of carbon by putting the carbon in contact with the iron sponge, accompanied by accelerating agents, such as are used for case-hardenin g.

To enable others skilled in the art to use my invention, I will now proceed more especially to describe the same.

I take the iron sponge and intimately mix therewith five per cent., by weight, of carbonaceous matter, such as finely-pulverized charcoal and one-half of one per cent. of an accelerating agent, such as yellow prussiate of potash. The mass is then, while cold, compressed by suitable means into blooms having sufficient cohesion to be charged into a heatingfurnace, (auxiliary to the open-hearth meltingfurnace,) where they are brought to a red heat first, and subsequently raised to as much higher heat as is found necessary. From the auxiliary or heating furnace the blooms are charged into the melting-furnace, test being taken from time to time in the usual way, and blooms of carburized or uncarburized iron sponge employed, as indicated by the tests, until the mass is ready for the spiegeleisen or ferro-manganese, after which the operation is conducted in the usual manner.

Upon withdrawing the blooms from the auxiliary or heating furnace, and transferring them to the melting-furnace, the auxiliary furnace may be charged with a new lot of blooms, to be heated while the previous lot is being melted down, and thus the process be made continuous.

It will be evident to those skilled in the art that the several steps set forth may be somewhat varied, especially as regards the casehardening ingredients, (of which prussiate of potash is simply mentioned as an example,) and the proportions thereof and of the charcoal used, without departing from the spirit of my invention, the essential feature of which is the method of imparting the carbon to the iron.

The advantages of my improved process are as follows: First, the economy resulting from substituting the iron sponge, which can be produced at less cost than suitable cast-iron; and, second, the improvement in quality of the cast-steel, the iron sponge containing absolutely no silicon, while the pig-iron always contains a notable quantity. The open-hearth steel heretofore produced has always had this advantage as compared with crucible steel, that pig-iron was a necessary element in its manufacture, while crucible steel, for all fine purposes, is made without it. 

